A microphone user often depends on a testing device to select the microphone that is most suitable for him or her. The testing device is ubiquitous in a variety of places, such as nightclub, conference floor, bazaar, etc. The conventional testing device is used in conjunction with a sound reproducing system which may comprise a sound mixer, amplifiers, loud speakers, and the like. It is therefore readily apparent that the conventional testing device is not cost-effective and that the conventional testing device is incapable of testing objectively the tone quality of a plurality of microphone in view of the position nonuiformity or the circuit error of the tone quality control of the sound mixer. In addition, the precision of the conventional testing device is often compromised by the on-site noise.